Skip to content

Latest commit

 

History

History

eg_25_async_io

Folders and files

NameName
Last commit message
Last commit date

parent directory

..
test
test
 
 
Makefile
Makefile
 
 
README.md
README.md
 
 
load_module.sh
load_module.sh
 
 
main.c
main.c
 
 
main.h
main.h
 
 

README.md

asynchronous_notification

Asynchronous notification is a mechanism to notify the user program that interested I/O is ready to operate. Using poll or select is a sort to synchonous of I/O notification, the process will be blocked on the call to poll or select function until the underlaying I/O device is becoming ready again. The CPU is occupied during the entire period, no other operations can be taken. However, in asynchronous notification, the CPU can be handled to other process for other tasks, when the I/O is ready, a signal(usually SIGIO) is send to the process which interrupts the current process to let the I/O event can be processed in time.

In this example, we write a simple device driver which implements the basic asynchronous notification mechansim. When some processes write any data to the device file, the process who set the file descriptor as async will receive the SIGIO signal. The process could catch this signal and check the file descriptor state for reading or writing.

build the module

To build this module, execute:

make KERNELDIR=/path/to/kernel/source/dir

If you have already set and exported KERNELDIR environment variable, simply execute make is enough.

If neither KERNELDIR environment variable nor KERNELDIR option of make are set, the current running kernel will be built against.

Usage

Copy load_module.sh and async_notify.ko files to the target machine, then run:

sh load_module.sh

test the module

To test this kernel module, first compile and copy the test program loacated in test directory to the target machine. Then, after the module is successfully loaded, run the test program async_notify.out.

The program async_notify.out registers the signal handler for SIGIO signal, which will be invoked when the file descriptor is notified. In the signal handler, we add 1 to the global variable each time the handler is invoked. The global variable will be checked in the loop in main() function, and set it to 0 if it is greater than 0. In this case, the read() function will be called on the file descriptor for read data from the valid file descriptor.

Sample output is:

no signal, continue!;
no signal, continue!;
no signal, continue!;
no signal, continue!;
signal is catched
Hello World!

¶ The end